6:2

class Solution
{
    public:
        int countWords(string list[], int n)
        {
          map<string,int>mp;
          for(int i=0;i<n;i++)
           {
             mp[list[i]]++;
           }
           int count=0;
           for(auto u:mp)
           {
               if(u.second==2) count++;
           }
           return count;
        }

};